Method of preserving coated abrasives



Patented July 30, 1940 UNITED STATES PATENT OFFICE METHOD OF PRESERVING COATED ABRASIVES' tion of Massachusetts No Drawing. Application December 27, 1938, Serial No. 247,828

1 Claim. 101. 51-281) .Therinvention relates to coated abrasives and lnvolvesa method of preserving them from deterioration, and with regard to its specific features to preservingglue bonded coated abrasives, 5 particularly sandpaper.

One object of the invention is to provide a facile method for the preservation of glue bonded sandpaper. Another object of the invention is to provide a facile method for the preservation ofglue bonded abrasive cloth. Another object of the invention is to provide a method of the type indicated which will not interfere with transportation of the abrasive in roll form or storage thereof under varying conditions. Another object of the invention is .to provide a method which is applicable alike to cut sheets, to discs, and to coated abrasives in rolls. Another object of the invention is to provide a method for the preservation of sandpaper or abrasive'cloth from changes in theatmosphere which also effectively preserves the abrasive from mechanical injury and the effects of sunlight. Other objects will be in part obvious or in part pointed out hereinafter.

eral steps andrelation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the applicatio'n of which will be indicated in the following claim.

The coated abrasives which my invention deals with may be either paper backed, cloth backed, or have a backing consisting of a combination of cloth and paper, and theabrasive may be of any type in comminuted form. So far as the more specific features of the invention are concerned, the bond holding the comminuted abrasive to the backing is a protein, which includes casein and glue, but more specifically my invention relates particularly to preserving the efliciency and life of coated abrasives in which the bond is glue. Animal glues, such as hide glues, are preferred adhesives but the glue may include dextrines or starches, and casein, where used, may be embodied in various mixtures including casein. For example, the method has particular value in preserving glue bonded sandpaper from the ravages of heat, moisture, sunlight and mechanical inury. I I0 The abrasive itself may be of any type, examples of which are alumina in its several forms including electric furnace fused alumina, natural corundum and emery, also any of the hard carbides, especially silicon carbide, also any of the varieties of garnet and any of the varieties Theinvention accordingly consists in the sevv of quartz. Crushed glass which is used to a considerable extent in certain parts of the world may be the abrasive and, in fact, anyother type. of abrasive comes within the scope of the present invention. 5

The backing may be either of the woven or felted type, or a combination of the two; that is to say, the backing may be a cloth backing or it may be of any type of paper, parchment, vulcanized fibre or a combination of a cloth 10 backing and a felted backing, such as paper, parchment, vulcanized fibre and the like.

For the manufacture of the coated abrasive, any known method or process may be used. For example, the sheet is customarily drawn off a roll 16 and has the adhesive applied thereto by a roller and the abrasive applied thereto either by gravity or an electrostatic field. However, the method of the present invention may be applied to preserve coated abrasives of the type inicated however they are produced.

In the manufacture. of coated abrasives, it is customaryto. take the sheet into a drying room where it is festooned and allowed to dry for a number of hours. The process of the present 25 invention may start after the drying or the drying room may be controlled so that the desired conditions will exist at one end of the room.

I provide a room with controlled humidity. Preferably I maintain the room at a temperature of about 70 F. and in this room I maintain a relative humidity of However, humidities other than 45% may be adopted, this being within the preferred range which is from 35% to although the method of the invention 35 may be carried out with the humidity in the range between 30% and While I prefer a temperature of about F., a comfortable temperature for working and carrying out the operations of my process, it should be understood that the important point in my invention is to bring the coated abrasive to the correct moisture content. A correct moisture content will be obtained .in the coated abrasive if the coated abrasive brought to equilibrium 45 with an atmosphere of 30 to 60% relative hu- The foregoing gives the range of humidities according to the present invention and the humidity may be maintained by apparatus which is now readily available on the market so I shall not describe the same herein. Any apparatus for controlling the humidity of the room may be used. I have given the ranges of humidities above, but it should be understood that in carrying out my invention, it is desirable to select a particular humidity and maintain the room at that humidity within the limits of the capability of the apparatus. Apparatus now available will establish humidity in areasonably large room provided with circulating fans within a range of plus or minus 5%.

Immediately after the manufacture of coated abrasive material, I introduce it into such a room. I maintain it in the room for a long enough time so that the glue or other adhesive will come to equilibrium with the humidity of between 30% and 60%. The coated abrasive may be in any convenient form, such as sheets, discs or rolls. Preferably I take the coated abrasive, for example sandpaper, in roll form into the room with controlled humidity.

In lieu of the final drying and conditioning of the coated'abrasive immediately after its manufacture, I may store the coated abrasive in an atmosphere suitable for the preservation of the bond, that is, in an atmosphere with a humidity range within the limits of 30% and 60%, preferably about 45%, and subsequently cut the coated abrasive into the desired forms, such as rolls, sheets, discs and the like in a controlled atmosphere for sealing or packaging to preserve he bond, as explained hereafter.

I further provide air-tight containers of any suitable type. Large sized cylindrical sheet metal cans are preferred. Preferably they should have a joint with a long overlap. It is highly desirable that they should be of a size to hold the coated abrasive with a minimum of air space left. I place a roll of coated abrasive in such a can and place the. cover in position. Or, on the other hand, in case the coated abrasive is in small flat sheets, I place these in the can. Having put the cover on, I seal thejoint, which maybe done as follows: Adhesive tape is wound around the joint, overlapping so that one part is stuck to the cover and the other part is stuck to the bottom of the can. This is then brushed with molten parafiine maintained at a temperature of about C. Any other suitable means of sealing such containers may be used.

The coated abrasive is now ready for shipment and will maintain its efiiciency under many vicissitudes of change of humidity in the outside atmosphere and change in temperature.

I have found that moisture-sensitive adhesives, such as animal glues, customarily used in the manufacture of coated abrasives, lose much of their efficiency if the humidity is not kept within the range of 30% to 60%. The deterioration is particularly rapid in the case of the coarser grits used in the manufacture of coated abrasives. I have further found that reasonable temperature changes such as are generally encountered in the handling, storageand use of coated abrasives do not cause serious deterioration if the humidity is maintained within the range mentioned. I have also found that rapid or frequent changes in humidity, especially outside of the range of 30% to 60% relative humidity, cause rapid deterioration of glue bonded coated abrasives. The sealing up of the coated abrasive material in an ter, within a closer range of 35% to 55% relative humidity, these animal glues have an excellent balance between strength and elasticity and are among the most eificient adhesives known for the manufacture of coated abrasives. If the humidity becomes too high, that is, if the conditions are such that the glues take up too much moisture, they become soft, weak and too elastic. If used in such a condition, the coated abrasive will give low production and be relatively ineflicient. The sealing of the coated abrasive when it contains the correct amount of moisture,

, therefore, is a safeguard against low production and inefiiciency resulting from the glue containing too much moisture. On the other hand, if the humidity falls too low, the glue gives up moisture and when the glue has a deficiency of moisture, it becomes hard and brittle and inelastic. There is also considerable shrinkage of the glue due to loss of moisture. A combination of shrinkage of the glue and brittleness or lack of elasticity results in the glue pulling away from the grains so that'they are no longer efiiciently held and they shed rapidly in the abrading oper ation. The sealing of the coated abrasive while it contains the correct amount of moisture, therefore, prevents deterioration of bond due to excessive loss of moisture. This is especially important during the colder months of the year where artificial heat is used without a corresponding artificial humidification.

With a given relative humidity in a sealed container at a given temperature, a change in temperature of that container will cause a change in the relative humidity. At the time of sealing the coated abrasive in the container, there is equilibrium between the amount of moisture in the coated abrasive and that in the air. Both the glutinous adhesive and the'paper or cloth backings are hygroscopic materials containing considerable moisture at any reasonable humidity. A rise in temperature within the container tends to reduce the relative humidity of the air but concurrently with the rise in the temperature the adhesive and the backing give up some of their moisture. This moisture cannot escape but acts as a back pressure to prevent continued loss of moisture from-the adhesive and the backing. In order to maintain the closest possible limits for relative humidity within the container, it is desirable that the container be filled as full as possible with coated abrasives and, therefore, contain as little air as possible. While this is true, it is also true that the adhesive and backing contain relatively large quantities of water per unit of volume as compared with the water contained by an equal unit of volume of air. Therefore, even though the container is not filled as full as possible with the coated abrasive, I am enabled to maintain favorable storage conditions and prevent a large part of the deterioration that has heretofore taken place in coated of change in the absorbed moisture in the glue bondcr other bond. From the standpoints of efliciency of packaging and protecting the con-,.

tents from deterioration, I prefer that at least 50% of the free space within the container be occupied by the coated abrasive material or cushioning material which would serve to reduce the quantity of air within the container and keep the quantity of moisture in the air low as compared with the quantity of moisture in the coated abrasive. 'My procedure by actual test considerably prolongs the life of 'the coated.

abrasive material.

Tests demonstrating the effectiveness of the method include the following.

Samples of glue bonded sandpaper were placed in a glass jar with a rubber gasket, filling the jar to the extent of'70% of the space therein. The atmosphere in the jar was approximately '75 .F. and had a relative humidity of 50%. Other samples were placed in an open container alongside the glass jar. All samples were subjected to a temperature of 140 Fgfor several days. At the end of that time the samples in the glass jar were still in salable condition, whereas those in v the open jar had deteriorated to the point where they were unsalable.

Three small rolls of No. 40 grit size sandpaper were handled as follows z -The first was unwrapped. The second was wrapped in two layers of Cellophane, and the third was sealed in a glass jar having an atmosphere of approximately 50% humidity, taking up 70% of the volume of the jar. These rolls were then placed in a hot room having a temperature of about 125 F. and approximately 15% relative humidity for two weeks. They were then placed in an ordinary household electric refrigerator for a period of one week. They were then subjected to the temperature of 125 F, at 15% relative humidity for three days.

A wear test was made by scratching with a pick and counting the strokes required to wear through 3 the layer of glue. The following table indicates the result:

Strokes Unwrapped r011 30 Roll in Celloph 60 Roll in glass jar 100 A number of packages of sandpaper were sealed in tins of a size such that 80% of the tins were occupied by the packages, the atmosphere in the tins having originally a relative humidity of about 50% and a temperature of 70 F., and were placed in a normally heated ofiice located in a latitude approximate]; 45 North in the eastern part of the United States. Further packages of the same kind of sandpaper were stored in the same place i but were unsealed, that is, they were not in tins nor were they sealed from changes in atmospheric conditions. These packages were kept inone place for approximately a year. At the end of the year the tins were opened and-the papertaken therefrom was compared with the paper of the unsealed packages. The latter had'deteriorated to a considerable extent whereas the former were in excellent condition.

My invention also contemplates using suitable atmospheres other than air such as, for instance, nitrogen containing a suitable quantity of moisure.

It will thus'be .seen that there has been provided by this invention a method in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of theabove invention and as many changes might be made in the embodiment above set forthpit is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

The method of preserving a flexible sheet abrasive material coated with a layer of abrasive by an adhesivebond and which bond is a protein,

which consists in providing an atmosphere of between 30% and relative humidity placing the flexible sheet abrasive material in said atmosphere until it comes to equilibrium therewith in its moisture content, then placing said mate- 

